Research On Construction Control Analysis And Prediction Method Of Suspender Replacement Of Tied Arch Bridges

With the increasingly prominent problem of vehicle overload,coupled with many factors such as design and construction defects,improper operation and maintenance,and material performance degradation of tied arch bridges,the structural safety hazards caused by suspender diseases are gradually exposed.At present,a large number of inservice tied arch bridges are facing the problem of suspender replacement.However,there is no detailed theoretical system of suspender replacement construction control in China.Therefore,it is very important to carry out more detailed research on suspender replacement method and construction control of tied arch bridges.This paper is based on the suspender replacement project of a middle-bearing concrete filled steel tube(CFST)tied arch bridge,and the following work is mainly carried out.First,the spatial finite element model of the whole bridge is established according to the design information of the CFST tied arch bridge.Reasonable completed cable forces are determined by “zero displacement method” and “minimum bending strain energy method”,and cable forces at construction stage are determined by “direct analysis of unclosed mating force” and “direct iteration method”.By comparing the reasonable cable force of the bridge with the measured cable force before the replacement of the suspender,it shows that there is a big deviation between the measured cable force and the designed cable force,the performance degradation of bridge structure is obvious,and the full bridge’s suspenders need to be replaced.Then,based on the principle of influence matrix,the optimization model of suspender replacement cable force is established.The construction control analysis method of suspender replacement with unequal step transfer of cable force is proposed,and the construction simulation of suspender replacement is carried out.The cable force of new and old suspenders,the cable force of temporary suspenders and the variation law of bridge deck alignment in the process of suspender replacement are studied,and compared with the simulation results of equal step length transfer of cable force.The results show that the vertical deformation control index with 5mm as the control point can effectively inhibit the cracking of concrete bridge deck in the process of suspender replacement with unequal step transfer of cable force.The whole replacement process needs to improve the bridge deck for 6 times,including 12 grading conditions.The maximum cable force of the whole bridge appears in the hanger S10,and the cable force value is 1279.86 k N.At this time,the hanger X12 and S9 are just completely removed.The maximum relative displacement of the control point of the replaced suspender is 15 mm,which leads to the large fluctuation of the bridge deck alignment and the cracking of the concrete bridge deck.Therefore,the cable force control method of the suspender replacement with unequal step transfer has less influence on the original structure and higher construction safety.After replacing the suspender with the suspender replacement method of unequal step transfer of cable force,the cable force of the whole bridge is close to the objective cable force,and the long-term service performance of the bridge has been effectively consolidated.Next,to explore the relationship between the bridge deck alignment and different construction parameters during the construction process of suspender replacement,the sensitivity of the influencing factors of the relative elevation deviation of the outer deck of the replaced suspender is analyzed this paper.It is found that the main influencing factors causing the deviation between the relative elevation of the outer deck of the replaced suspenders and the design elevation are: the cable force deviation of the replaced suspender,the cable force deviation of the temporary suspender,the cable force deviation of the adjacent suspender,and the temperature gradient deviation of the tie beam section.Based on the D-optimal experimental design method of response surface,the relationship between the relative elevation deviation of the outer deck of the replaced suspender and each factor is fitted by the second-order polynomial regression equation,and the fitting accuracy is high.Finally,the Bayesian network is built by taking the cable force deviation of the replaced suspenders,the cable force deviation of the temporary suspenders,the cable force deviation of the adjacent suspenders and the temperature gradient deviation of the tie beam section as the root node,and the relative elevation deviation of the outer deck of the replaced suspenders as the leaf node.It is assumed that the four root nodes obey the Gaussian distribution and the edge probability distribution is discretized.The initial training samples are obtained by Monte Carlo(MC)sampling algorithm,and the initial probability table of Bayesian network is determined based on the maximum likelihood estimation method.After that,the evidence samples of each working condition are continuously added to form new training samples,which are used to train the Bayesian network model,update the posterior probability distribution of parameters.Furthermore,the change of bridge deck elevation in each working condition of suspender replacement is predicted.The results show that after working condition 3,the deviation between the predicted value and the actual value is basically within ±10 %,and the prediction accuracy is high,which can provide a theoretical reference for the bridge deck alignment control during the construction process of boom replacement.